1. Field of the Invention
The invention relates to instrumentation for determining a grade line. In particular, the invention relates to measuring instrumentation for use in cooperation with grade stakes for determining the grade within a ditch wherein pipe, or the like, may be laid.
2. Prior Art
Where water or other fluid is to flow through a pipeline under the influence of gravity, it is necessary that a proper grade be established on which the pipe shall be laid. Preliminary measurements are generally made by skilled workers, such as surveyors. These skilled workers determine the run, or line along which the pipe shall be laid. Grade marking stakes are usually placed in the ground along a line offset a given distance from the run line of the pipe. A ditch will be dug in which the pipe will be positioned. To assure that the pipe shall lie along the proper grade, the grade stakes are marked with a depth reading measured from the top of the grade stake. If the ditch is everywhere dug to the depth indicated by adjacent grade stakes, a pipe laid in this ditch will lie on the proper grade to assure the gravity flow of liquid along the pipeline.
Since the pipe must couple to input and output devices which may already be in position prior to the installation of the pipeline, it is usual practice for the surveyors to indicate on the grade stakes, the depth from the top of the grade stake to the fluid flow line of the pipe. Thus, in setting pipe within the ditch, the construction workers will have to bear in mind the thickness of the wall of the pipe, or the pipe diameter, or both.
Because professional surveying equipment is so expensive, those skilled in the prior art have sought means for utilizing other, less expensive devices to serve the needs of those setting out grade stakes. Cotton in U.S. Pat. No. 3,170,239 utilizes a relatively inexpensive builders optical level to establish the run and then places a prism in the line of sight of the optical level to offset the line of sight as required to achieve the desired grade. Husby, in U.S. Pat. No. 1,231,162, provides a water level with an optical mount which will accommodate an optical device and permit its tilting to the degree necessary to establish the necessary grade for the run of pipe.
While the grade stakes are emplaced by workman of relatively high skill, the digging of the ditch and the placement of the pipe therein is generally assigned to workmen having less skill in matters of grade determination. Various devices have been conceived of, designed to aid these workman in placing the pipe at the proper depth and along the proper grade. Treloar in U.S. Pat. No. 1,476,340 discloses apparatus and method whereby several targets are positioned over the ditch in which the pipe is to be laid. A staff is placed upright with its bottom resting in the ditch. The workman sights over the staff and along a series of targets to test for proper grade alignment.
A more sophisticated technique for laying pipe on proper grade is disclosed by Trice in U.S. Pat. No. 3,591,926. Here a laser beam is positioned so as to transmit along the center line of the pipe run, the beam being tilted appropriate to the required grade along which the pipe run shall be established. The laser beam is positioned with the aid of a surveyor's instrument and a plumb bob on a surveyor's scale is utilized to establish the proper depth below the surveying instrument for the laser light source. The plumb bob is used to ensure that the line of the light beam passes through a point directly below the surveyor's sighting instrument.
A device for measuring the height of a quarry wall from the floor of the quarry is disclosed by Eldridge in U.S. Pat. No. 1,654,164. The device is actually a triangulation instrument which measures the slant distance from the instrument to the quarry floor. However, the tape which is utilized along the slant distance is calibrated so as to read the vertical distance from the top of the instrument to the floor of the quarry. Minor modification to the calibration of the tape measure would permit the readout to be referenced to the base of the triangulation device, which base could be established atop the surveyor's line stake.
While not necessarily pertinent to the establishment of grade lines, the disclosure of Olsen et al, U.S. Pat. No. 835,711, discloses a sighting device in which a mirror is utilized to rotate the line of sight through 90.degree.. Such an arrangement is incorporated in one of the preferred embodiments of the invention disclosed herein.
In actual practice, today's techniques require the workman to establish a level grade at the terrain surface between the grade stake and the edge of the trench in which the pipe is to be emplaced. A board is then emplaced on this leveled surface and the end of the board extended outward over the trench a distance equal to the offset of the pipe from the grade stake. While one workman holds the board in position, another makes the depth measurement from the base of the board to the bottom of the ditch. This practice is difficult and clumsy and often provides an inaccurate measurement of grade.
It is therefore an objective of the invention to provide a simple but accurate means for obtaining a proper grade line.
It is a further objective of the invention to provide means and method whereby a single, unskilled laborer, may accurately determine the proper grade within a ditch in which pipe is to be laid.
It is a particular objective of the invention to provide means for establishing a grade line which means are adaptable for establishing said grade line at the bottom of the ditch, at the flow line of the pipe, or at the top, outer surface of the pipe.
It is a specific objective of the invention to establish a horizontal line of sight a selected distance above a grade stake and to intersect that line of sight, at a prescribed offset distance, with a vertical, calibrated measuring device having an uncalibrated length at the base of the measuring device, which uncalibrated length is related to the distance selected in establishing the line of sight above the grade stake, the zero calibration of said vertical measuring device beginning immediately above said uncalibrated length.